Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 180955
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
455 AM EST Sun Feb 18 2018


.AVIATION...

MVFR stratus will scatter out during the morning hours as high
pressure and a warm front bring a change to the resident airmass
currently in place. The warm front will lift north through the area
around 14-18Z. Models forecast a fairly quick scouring out of the
remaining clouds below 10kft due to a very dry airmass moving in.
VFR conditions will last into the overnight period. A surge of
moisture ahead of a slow moving frontal boundary tracking east
across the Midwest will then provide a chance of rain showers Monday
morning.

For DTW...After MVFR stratus scours out late this morning, VFR
conditions will hold through most of the overnight with southerly
warm air advection occurring. Chance of rain showers begins after
09Z thus will include MVFR CIGs/VSBYs at this time.

/DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 ft this morning. Low after 16Z.
  moderate after 09Z Monday morning.

* High for ptype as rain starting Monday morning.

&&

.PREV DISCUSSION...
Issued at 317 AM EST Sun Feb 18 2018

DISCUSSION...

Upper heights will rise significantly today as shortwave trough
races east of the region and broad upper troughing over the western
CONUS begins to take shape with time. At the surface, high pressure
will shift to the eastern seaboard today with a low pressure system
develops over the northern plains/upper midwest as initial shortwave
energy ejects northeastward from the developing western trough. This
will lead to a steady increase in southerly flow today, and with a
fair amount of sunshine expected, temperatures should respond nicely
and climb into the upper 30s to lower 40s despite the fair amount of
snow cover that still persists over much of the forecast area.

The lead shortwave and associated low pressure system to the west
will track through the upper midwest and northern Great Lakes late
today through tonight, dragging a warm front north towards the area
by early Monday morning. Strong theta-e advection up the surface of
the front with southwesterly flow at the H85 level on the order of
40 to 60 knots. This will lead to a rather rapid expansion of rain
showers north/northeast into the area Monday as the front continues
to edge north into the southern Great Lakes. An initial dry airmass
over the area will lead to some evaporative cooling along the north
edge of the precipitation shield, which could allow just a bit of
ice pellet mixture. However, given the main expansion of rain holds
off until the 12z-16z time frame, do not expect this to be noteworthy
and will maintain an all rain forecast.

Temperatures will increase steadily throughout the day as the warm
front lifts north with widespread 50s anticipated by late afternoon
into the evening. Only far northern portions of the forecast area
may stall in the 40s as the progress of the warm front northward
slows considerably late in the day.

During this whole time, the main shortwave that will eject into the
area from the western trough will be lifting from the four corners
region into the plains, leading to additional cyclogenesis on the
lee of the Rockies. This pattern will maintain a strong south to
southwest flow into the area (the first with a solid feed from the
Gulf of Mexico in quite some time). So, moisture with this event
will be impressive with precipitable water readings to at least
1.25", H85 dew points to 10C and surface dew points in the 50s.
Meanwhile, temperatures will climb into the 60s over a large part of
the forecast area. These readings should top records for DTW and
FNT, but MBS may fall short depending on the exact frontal position
by Tuesday afternoon.

Hence, rainfall chances will remain high Monday night into Tuesday
with an increasing chance of locally heavy rainfall. While the whole
area stands a very good chance of rain, the best focus during this
time frame will be over the north near the stalled warm frontal
boundary. Some chance of thunder will also remain as Showalter
indices drop to around zero, denoting something of a neutral
elevated stability regime.

These conditions persist into Tuesday night, but the passage of the
surface low to the north of the area will drive the frontal boundary
gradually southeast overnight into Wednesday morning, focusing best
rainfall further and further south. All told, 1 to 2 inches of rain
can be expected in many area with upwards of 3 inches not out of the
question locally (where most persistent frontal forcing becomes
anchored).

The passage of this system will lead a cool down during the middle
of next week with temperatures in the 30s and 40s by day and 20s by
night. However, the overall western CONUS trough/eastern CONUS ridge
configuration in the upper level pattern does not change much. So,
after a cool (and dry) interlude in the wake of this system), some
moderation in temperatures back well in the 40s to near 50 appears
pretty likely in the Friday/Saturday time frame with a renewed
chance of widespread precipitation heading into next weekend.

MARINE...

Westerly winds will veer to southerly this afternoon in the wake of
a warm front that will lift through the region. The warm front is
associated with a low pressure system that will track through the
northern Great Lakes tonight. Wind gusts will approach 30 knots for
a few hours this evening behind the front. A frontal boundary will
then get laid out across the central Great Lakes and stall there
through mid week. Several low pressure systems will track along this
boundary through the early part of the week. Location of the front
and fluctuations in it`s placement across the Lake Huron basin will
lead to rapid changes in wind speed and direction through mid week.

HYDROLOGY...

A strong warm and moist advection pattern will begin Monday and
persist through Wednesday ahead of a slow moving front. This warming
trend will result in a full melt off of present snow cover across
southeast Michigan. Several periods of rainfall can be expected
during this time with widespread rainfall totals of 1-2 inches over
the course of Monday to Wednesday. Taking into account the
possibility of convection, some locations could end up with rainfall
amounts nearing 3 inches. There is still some uncertainty with where
the higher rainfall amounts will fall due to potential shifts in
frontal positioning and location of convection. While the melting
snow will unlikely be enough to support flooding, the potential for
rainfall in combination with the snow melt could cause some rises in
area rivers and streams. Ice breakup on area rivers and streams
cause by warmer temperatures will also be something to keep an eye
on, which could exacerbate any local flooding issues.

CLIMATE...

Record high temperatures will be possible across much of southeast
Michigan Tuesday. Here is a look at record high temperatures for
Tuesday, February 20th:

Detroit     63 (2016)
Flint       61 (1930)
Saginaw     62 (1930)

With the high moisture content, good chance to break the high
minimum records for February 20th as well:

Detroit     47 (1930)
Flint       45 (1930)
Saginaw     46 (1930)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....DRK
DISCUSSION...DG
MARINE.......DRK
HYDROLOGY....DRK
CLIMATE......DG


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at www.weather.gov/detroit.



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